The brain processes and stores information by constantly adjusting the strength of connections between its neurons. In order to adjust the strength of these connections, called synapses, the neurons have to synthesize new proteins. Proteins can be synthesized in the soma of the neuron and then travel through dendrites to reach the synapses. Alternatively, proteins can be synthesized within the dendrites close to the synapses. This dendritic protein synthesis provides a rapid and efficient way of modifying the strength of single synaptic connections. Dendritic protein synthesis is important for normal brain development and cognitive functions. When dendritic protein synthesis is impaired, for example in Fragile X Syndrome, it causes severe neurodevelopmental and cognitive deficits. Despite its importance, there is an incomplete understanding of dendritic protein synthesis. A major remaining question is: which proteins can be synthesized in dendrites? This project will test and apply novel tools that can answer this question. The tools allow for the selective isolation of ribosome-bound messenger RNA (mRNA) from in-vivo dendrites. Since ribosomes bind to mRNA in order to synthesize proteins through a process called mRNA translation, the ribosome-bound translated mRNA directly reflects which proteins are being synthesized. In order to completely characterize dendritic translated mRNA, this project will use next-generation sequencing in order to sequence each mRNA molecule within the sample (RNA-Seq). Knowing the sequence of each dendritic translated mRNA molecule not only answers the question which proteins can be synthesized in dendrites, but also provides insights into the specific protein isoforms that are synthesized. The sequence data generated by this project can also be used to discover RNA motifs that are shared by groups of dendritic mRNA. Some of these motifs could regulate the transport of mRNA into the dendrite or the translation of mRNA within the dendrite. The insights into dendritic protein synthesis generated by this project will aid the development of treatments for brain disorders associated with impaired dendritic protein synthesis. PUBLIC HEALTH RELEVANCE: The brain constantly adjusts the strength of neuronal connections called synapses through a process that requires the synthesis of new proteins. Much of this protein synthesis takes place close to the synaptic connections in a part of the neuron called the dendrite, and impairments in this dendritic protein synthesis can cause impairments in brain development and cognitive function. This project will develop and use novel tools for determining which proteins are synthesized in dendrites, and will thereby generate knowledge that can be used to develop treatments for certain brain disorders like Fragile X Syndrome.